1. Technical Field
The present invention relates to a semiconductor device provided with an electrical fuse.
2. Related Art
Conventional semiconductor devices are known where a fuse is mounted so that a process can be carried out, for example the fuse can be cut to adjust the resistance value or separate a defective element, which is thus replaced with a normal element.
In order to provide a highly reliable semiconductor device where such a process can be carried out, it is necessary for the fuse to be cut without failure. Therefore, the fuse disclosed in Japanese Laid-Open Patent Publication 2005-57186 has been proposed.
As shown in FIG. 5, Japanese Laid-Open Patent Publication 2005-57186 discloses a fuse having a current flow-in terminal 902, a current flow-out terminal 901, a pair of fused via portions 903 and 904, and an electrode pad 905.
When a current flows through the fuse between the current flow-in terminal 902 and the current flow-out terminal 901, either of the pair of fused via portions 903 and 904 is fused.
Thus, a pair of fuses via portions 903 and 904 is provided, so that two regions which may fuse when a current flows are formed so that the fuse can be cut without failure, and it is considered that the reliability of the semiconductor device is high.
Here, in FIG. 5, the symbol 906 indicates a semiconductor substrate, and 907 and 908 indicate interlayer insulating films.
The present inventor has recognized as follows. The technology described in Japanese Laid-Open Patent Publication 2005-57186, however, has the following problems.
When a current flows between the current flow-in terminal 902 and the current flow-out terminal 901, electrons flow into the pair of fused via portions 903 and 904 in different directions relative to the up-down direction of the vias. Thus, in the case where the direction in which electrons flow in is different, the cut state is different between the fused via portions 903 and 904, and therefore there may be inconsistency in the resistance value after the fuses are cut.
In the case where a fused via portion 903 or 904 is cut through electromigration, for example, a void B is created in the fused via portion 904 in the vicinity of the electrode pad 905 when one fused via portion 904 is cut, as shown in FIG. 6A. This void B is created so that the conductor forming the electrode pad 905 would not move toward the fused via portion 904 because the electrode pad 905 is covered with a barrier metal (not shown), and thus the electrode pad 905 itself is not cut, and the conductor forming the fused via portion 904 is pushed.
In the case where the other fused via portion 903 is cut, as shown in FIG. 6B, a void B is created in the electrode pad 905 in the vicinity of the fused via portion 903.
Thus, the cut state may be different between the fused via portions 903 and 904, and in addition the ease of cutting is different, and therefore there may be inconsistency in the resistance value after the fuses are cut.
Here, there is inconsistency in the resistance value after the fuses are cut due to the difference in the direction in which electrons flow, not only in the case where the vias are fused through electromigration, but also in the case where the vias are cut in accordance with a so-called “crack assist method”.